Mobile terminated call improvements

ABSTRACT

In one aspect, a method for a packet gateway node (PGW) is disclosed. The PGW being adapted for (a) communicating with at least a serving gateway node, SGW, (b) receiving and forwarding downlink data packets to a user entity, UE, and (c) communicating with a mobility management entity, MME. In one embodiment, the method comprises: the PGW, when receiving a downlink user plane data packet destined for the UE on a Packet Data Network, PDN, connection associated with a restarted SGW, determining if the PDN connection has not yet been relocated to a new SGW, and, if so, selecting at least one SGW from a set of SGWs including the restarted SGW or another SGW and transmitting a control plane signal to at least one of the selected SGWs, the control plane signal identifying at least the UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/136,187,filed on Apr. 22, 2016 (published as US 20160242225) (status pending),which is a continuation of application Ser. No. 14/585,325, filed onDec. 30, 2014 (now U.S. Pat. No. 9,326,312), which is a continuation ofapplication Ser. No. 13/458,519, filed on Apr. 27, 2012 (now U.S. Pat.No. 8,929,335), which claims the benefit of U.S. Provisional PatentApplication No. 61/480,453, filed on Apr. 29, 2011. The above identifiedapplications and publications are incorporated by this reference hereinin their entirety.

TECHNICAL FIELD

This invention relates to the field of handling downlink data intelecommunication networks. More particularly, the invention pertains toEvolved Packet Core, EPC, System Architecture Evolution, SAE, systems inwhich a serving gateway node may be subject to restarting.

BACKGROUND

Some key elements of the SAE/EPC network have been dealt with in thefollowing references: [1] TS 23.236: Intra-domain connection of RadioAccess Network (RAN) nodes to multiple Core Network (CN) nodes; [2] TS23.401: General Packet Radio Service (GPRS) enhancements for EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) access; [3] TS24.301: Non-Access-Stratum (NAS) protocol for Evolved Packet System(EPS); Stage 3; [4] TS 23.007: Restoration Procedure; [5] TS 29.274:3GPP Evolved Packet System (EPS); Evolved General Packet Radio Service(GPRS) Tunnelling Protocol for Control plane (GTPv2-C); Stage 3; [6] TR23.857.

With the migration towards all IP (Internet Protocol) networks, allmobile traffic (voice and data) will be carried on the packet corenetwork step by step. In FIG. 1, the procedure in an EPC network forMobile Terminating (MT) voice service, when the UE is in Idle state isshown according to 3GPP TS 23.401, chapter 5.3.4.3. The mobileterminated traffic can be voice, data or multimedia traffic. In thisprocedure, the following events may be undertaken: (101) The UserEntity, UE, attaches and registers in the SAE/EPC network. (105) The PDN(Packet Data Network) Gateway, P-GW, receives a data packet addressed tothe UE (IP address) and forwards the data packet to the Serving Gateway,S-GW, via the corresponding GTP (GPRS Tunnelling Protocol) tunnel of theUE. (108) S-GW sends Downlink Data Notification to Mobile MobilityEntity, MME. (110) MME replies to S-GW with Downlink Data NotificationAck (Acknowledge). (112) UE location is known by MME with an accuracy ofthe serving Tracking Area. MME pages UE in the Tracking Area. (114) WheneNode B, eNB, receives paging messages from the MME, the eNB initiatesPaging procedure over the air. (116) Upon reception of pagingindication, the UE initiates UE triggered Service Request procedure(specified in TS 23.401) as the paging response. (120) The downlink datais sent to the UE.

MT Call Problem in Case S-GW of Restart:

According to the current mechanism described in 3GPP TS 23.007, when aP-GW/MME/SGSN detects that a peer S-GW has restarted, it shall deleteall PDN (Packet data Network) connection table data/MM bearer contextsassociated with the peer node that fail as well as freeing any internalPGW/MME/SGSN resources associated with those PDN connections. Sincethere are no bearer/MM (Mobility Management) contexts in the PGW, themobile terminated service can not be delivered to the UE for a longtime.

TR 23.857 proposes the following alternative solution to recover thebearer and MM contexts after detection of a SGW failure:

(1) The MME/S4-SGSN (Serving GPRS Support Node) and PGW maintain thebearers and MM contexts after detection of SGW failure. If theMME/S4-SGSN detects the SGW failure or restarts by referring to restartcounter, instead of removing associated resources, the MME/S4-SGSN andPGW maintain the bearers and MM contexts. The MME/S4-SGSN needs to knowwhether the PGW supports the capability to maintain the old PDNconnection after SGW failure or restarts, vice versa: which can belearned based on local configuration or new signalling between MME andPGW. This makes it possible for the MME/S4-SGSN to select a new SGW forthe UE.

(2) The MME/S4-SGSN selects a new SGW for the ECM_IDLE (EPS ConnectionManagement-IDLE) UE. The MME/S4-SGSN selects a new SGW for the ECM_IDLEUE based on the last visited TAI/RAI (Tracking Area Identity/RoutingArea Identity). Then MME/S4-SGSN sends a Create Session Request messageto the new SGW to establish the bearer contexts. The new SGW will send aModify Bearer Request message to the PGW to update the bearer context inthe PGW.

(3) The MME/S4-SGSN releases S1/Iu resources and selects a new SGW forthe ECM_CONNECTED UE. The MME/S4-SGSN firstly releases S1/Iu resourcesof ECM_CONNECTED UE. Then the MME/S4-SGSN will handle the UE in the sameway as for the ECM_IDLE UE.

However, considering typical load conditions, the inventors note thatthe above recovery can not be finished for all the UEs immediately. Incase there is an incoming MT (mobile terminated) call arriving at PGWbefore the recovery occurs, the MT call will fail according to the abovedescribed mechanism.

SUMMARY

It is an object of the invention to secure that mobile terminated callsare not lost, in particular in situations when e.g. a failing SGWrestarts.

This object has been accomplished by means of respective methods andnodes as well as by means of the signalling according to embodiments ofthe invention, namely as defined in the following:

A method for a packet gateway node, PGW (P-GW), being adapted forcommunicating with at least a serving gateway node, SGW (S-GW), the PGWbeing adapted for receiving and forwarding downlink data packets to auser entity, UE, the SGW moreover being adapted for communicating with amobility management entity, MME (MME/SGSN). The method comprises thesteps of when receiving a downlink user plane data packet (505) destinedfor the UE on a Packet Data Network, PDN, connection associated with arestarted SGW; determining if the PDN connection has not yet beenrelocated to a new SGW. If that is the case, selecting at least one SGW,that is, the restarted SGW or another SGW; transmitting a control planesignal to the selected SGW, the control plane signal identifying atleast the UE.

There is also provided a method for a serving gateway node, SGW, beingadapted for communicating with at least a packet gateway node, PGW, theSGW and being adapted for receiving and forwarding downlink data packetsto a user entity, UE, the SGW communicating moreover communicating witha mobility management entity, MME; comprising the steps of the SGW ifreceiving a control plane signal from the PGW identifying at least theUE, forwarding the control plane signal to a plurality of MME's the SGWis connected to or to a MME indicated in the control plane signal.

Moreover a method for a Mobility Management Entity is provided. The MMEbeing adapted for inserting its MME identity (MME ID) in a CreateSession Request signal or in Modify Bearer Request Signal.

Specific signals are provided according to embodiments of the invention.A signal for a 3GPP a serving gateway node, S-GW or a PDN gateway node,P-GW, or a Mobility Management Entity, MME, the S-GW being adapted forcommunicating with at least a PDN gateway node, P-GW, and a user entity,UE is provided. This signal is formatted as a Create Session Request foruse during attach and RAU/TAU/handover with SGW relocation procedure, orModify Bearer Request during inter MME/Serving Gateway Support Nodemobility procedure. The signal may comprise an information elementcontaining a Mobile Mobility Entity Identity, MME ID/Serving GatewaySupport Node identity, MME/SGSN ID.

There is also provided a signal for a 3GPP a serving gateway node, S-GW,or a PDN gateway node, P-GW, or a Mobility Management Entity, MME, theP-GW and S-GW being adapted for communicating with one another, the S-GWbeing further adapted for communicating with a user entity, UE, via amobility management entity, MME. The latter signal is being formatted asa GTP message such as Paging request or Downlink Data Notificationmessage with information elements corresponding to an InternationalMobile Subscriber Identity, IMSI, and/or a Mobile Mobility EntityIdentity, MME ID.

Additionally, a Packet gateway node, PGW (P-GW), is provided beingadapted for communicating with at least a serving gateway node, SGW(S-GW), the PGW being adapted for receiving and forwarding downlink datapackets to a user entity, UE, the SGW moreover being adapted forcommunicating with a mobility management entity, MME; the PGW beingadapted for, when receiving a downlink user plane data packet destinedfor the UE on a Packet Data Network, PDN, connection associated with arestarted SGW, determining if the PDN connection has not yet beenrelocated to a new SGW and if so selecting at least one SGW, that is,the restarted SGW or another SGW; transmitting a control plane signal tothe selected SGW, the control plane signal identifying at least the UE.

Also a Serving gateway node, SGW, is provided being adapted forcommunicating with at least a packet gateway node, PGW, the SGW andbeing adapted for receiving and forwarding downlink data packets to auser entity, UE, the SGW communicating moreover communicating with amobility management entity, MME; the SGW being adapted for, if receivinga control plane signal from the PGW identifying at least the UE,forwarding the control plane signal to a plurality of MME's the SGW isconnected to or to a MME indicated in the control plane signal.

Moreover, a Mobility Management Entity, MME is provided, the MME beingadapted for inserting its MME identity (MME ID) in a Create SessionRequest signal or in Modify Bearer Request Signal.

Further advantages of the invention will appear from the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art signalling diagram relating to a mobileterminated data transfer according to EPC/SAE,

FIG. 2 shows embodiments of a packet gateway, a serving gateway and amobility management entity according to the invention,

FIG. 3 shows an embodiment of a method for a packet gateway according tothe invention,

FIG. 4 shows an embodiment of a method for a serving gateway accordingto the invention and an embodiment of a method for a mobility managemententity according to the invention,

FIG. 5 shows a signalling diagram for a restarted serving gatewayaccording to the invention, and

FIG. 6 shows the PGW being updated with a mobility management entityidentity, MME ID, during Attach and Inter MME/SGSN mobility procedures,according to the invention.

DETAILED DESCRIPTION

MT Call Enhancements in Case of SGW Restart

According to an embodiment of the invention, MT call enhancements for aSAE/EPC network are provided. Embodiments of the invention may comprisethe following functionality, with reference to FIG. 5:

(1) In case of receiving a DL (Downlink) packet 505, c.f. FIG. 5, for aUE related to the restarted SGW before recovery of the UE bearer and MMcontexts—i.e. the PDN connection has not been relocated to a new SGW—thePGW sends a new GTP message 511 for example Paging Request or reuse theexisting GTPv2 message Downlink Data Notification message towards aselected SGW, which could be the restarted SGW 502 or an arbitrary SGW,if the bearer context (for which a downlink packet is received) has beenpreconfigured (to perform PGW initiated paging request) as furtherexplained in this invention based on the operators policies, which iseither based on internal configuration in the PGW—such as based on QCI(QoS (Quality of Service) Class Identifier), ARP (Allocation andRetention Policy) or APN (Access Point Name) etc.—or based on theinteraction with PCRF (Policy and Charging Rules Function).

Note that the PGW needs to know the MME/SGSN ID (IP address on thecontrol plane), therefore, during PDN connection establishment and interMME/SGSN mobility procedure, c.f. FIG. 6, the MME/SGSN ID should also bepassed to the PGW.

One problem is that the PGW may not be able to receive an updatedMME/SGSN ID during inter MME/SGSN intra SGW mobility procedures due toS5/S8 signalling may not always be available.

The following options may be used to solve this problem of receiving anMME/SGSN ID:

a). If Partial Failure feature is supported by MME/SGSN/SGW/PGW, the SGWwill use an Update PDN connection set request to update the MME/SGSN ID,such as using the existing IE “MME-FQ-CSID” which contains MME/SGSN ID(MME/SGSN IP address).

b). The SGW triggers S5/S8 signalling by using a Modify Bearer Requestto update MME/SGSN ID. However, this will create a lot of extra S5/S8signalling.

c). If the SGW receives paging from the PGW, it forwards a pagingrequest to all connected MME/SGSN's. If an MME/SGSN can not find the UEcontext corresponding to the IMSI included in the paging request, itsimply regards the UE as not being handled by it and rejects the pagingrequest. Consequently, the MME or the SGSN which is handling that UEwill perform paging. In this case, a new GTP message is thereforeprovided according to an embodiment of the invention to avoid MME/SGSNconfuse with the solution to MME/SGSN failure (See TR23.857).

Option c) implies some S11/S4 signalling during the paging, butconsidering the solution is a supplement to the existing SGW failuresolution where MME/SGSN will perform SGW relocation at the same time,the amount of paging requests should be largely reduced. Note: comparingoption b and c, is in fact a trade-off between increasing signallingover S5/S8 dring normal operation and increase signalling during SGWfailure and when PGW has received downlink data.

(2) The selected SGW relays 513 the received paging request 511, c.f.FIG. 5, from the PGW via an existing GTPv2 Downlink Data Notificationmessage or a new message towards an MME/SGSN or the MME/SGSN indicatedin the message by MME/SGSN ID.

(3) MME/SGSN initiates S-TMSI or P-TMSI paging 517 towards the concernedUE identified by IMSI as part of Network Initiated Service Requestprocedure.

(4) The MME/SGSN which performed paging using S-TMSI or P-TMSI willreceive Service Request from UE/empty LLC frame, then the correspondingPDN connection will be relocated in an SGW, and then updated in PGW.

(5) The PGW will forward the downlink packet (not shown) to the UE overa new user plane which is established during SGW relocation.

FIG. 2 shows an embodiment of a PGW, a SGW and a MME/SGSN according tothe invention.

The PGW comprises a central processing unit, PCU_P, a memory MEM_P andan interface unit IF_P comprising at least interfaces to the InternetG_(i)/SGi and a S5/S8 interface. The PGW may, in addition to thefunctionality explained in this document, comprise P-GW functionality asis known in the art.

There is moreover provided a SGW according to the invention comprising acentral processing unit, PCU_S, a memory MEM_S and an interface unitIF_S comprising at least an S11 interface, a S1 user plane interface anda S5/S8 interface, as well as a S4 interface. The SGW may, in additionto the functionality explained in this document, comprise S-GWfunctionality as is known in the art.

There is moreover provided a MME according to the invention comprising acentral processing unit, PCU_M, a memory MEM_M and an interface unitIF_M comprising at least an S1-CP interface, a S3 user plane interfaceand a S6a and S11 interface, as well as a S4 interface. The MME may alsocomprise MME functionality as is known in the art, in addition to thefunctionality explained in this document

The functionality of the PGW according to embodiments of the inventionshall now be dealt with referring to FIG. 3 showing an embodiment of amethod that may be implemented and carried out in the processor unitPCU_P in the PGW and conveniently be stored as software instructions inthe memory MEM_P, shown in FIG. 2.

In step 300, a user plane downlink data packet 505 destined for a userentity, UE is received.

The PGW determines whether the user plane packet is destined to arestarted SGW, step 301.

If not, the PGW simply forwards 306 the user plane packet to the SGW, asis the case in FIG. 1, step 106.

If yes, in step 301, it is—determined 302 if the PDN connection of therestarted SGW has not yet been relocated to a new SGW.

Optionally 303 it is determined whether policies allow PGW initiatedcontrol plane signalling, that is, whether—a bearer context, for whichthe user plane data packet has been received, is preconfigured forallowing PGW initiated control plane signalling, based on operatorpolicies, that is, allowing—transmitting (308) a control plane signal(511) to the selected SGW, the control plane signal (511) identifying atleast the UE.

If yes to the condition(s) in step 302/303, the PGW selects an arbitrarySGW, step 304. The selected arbitrary SGW may be the restarted SGW.Alternatively, all connected SGW's may be selected.

In step 308, the PGW transmits a control plane signal 511 with anidentification of least the UE, or UE context, and optionally anidentification of the MME to the SGW selected in step 304.

In FIG. 3, there is moreover shown how the PGW receiving a createsession request 614 or a modify bearer request 626 with a mobilitymanagement entity identity, MME ID, the PGW retrieves and updates 313this identity for subsequent use in the control plane signal 511.Likewise, upon receiving a Modify Bearer request with a MME ID, 312, thePGW stores the received identity. Further reference is made to FIG. 6.The PGW may moreover insert its PGW identity, PGW ID, in Create sessionresponse 616 and modify bearer response 628 messages.

In FIG. 4, the functionality of the SGW is demonstrated. FIG. 4 relatesto a method that may be implemented and carried out in the processorunit PCU_S in the SGW and conveniently be stored as softwareinstructions in the memory MEM_S, shown in FIG. 2.

The method for the SGW involves two parallel routines being carried out.

In the first routine, step 406, it is determined whether a control planesignal 511 is received identifying at least the user entity.

If so, it is further investigated whether a MME ID is provided, 408.

If a MME ID is provided, the SGW forwards the control plane signal 513to the identified MME, 410. On the other hand, if it is not the case,the SGW forward the control plane signal 513 to all connected MME's,412.

The second routine incorporates the step of receiving downlink data tothe user entity, 402. If so, a control plane Downlink Data Notificationmessage is transmitted to the MME in the same manner as shown in FIG. 1,step 108.

In FIG. 4, there is furthermore shown a MME according to the invention.The MME is inserting 413 its MME ID in a Create Session Request signal612 upon receiving 412 an Attach Request 610. Moreover, it is inserting413 its MME ID in a Modify Bearer Request signal 624 upon receiving 412a Tracking Area Update Request Signal 622. Further reference is made toFIG. 6. The SGW receives and forwards 414, the create session requestand the modify bearer request to the PGW.

An embodiment of the detailed MT call enhancement scenario in case of aSGW restart is illustrated in FIG. 5:

(1) Step 501: The UE attaches and registers in the SAE/EPC network.

(2) Steps 502, 503, 504: The SGW restarts and loses its UE contexts, forinstance after a short duration failure. MME, step 504, and PGW, step503, keep the UE contexts related to the restarted SGW and smoothlyre-establish the PDN/MM contexts of those UEs by selecting a new SGW,refer to 6.3.1.1 of TR 23.857. Another possibility is that of noimmediate re-establishment, instead only MO (Mobile Originating) and MT(Mobile Terminated) calls trigger a re-establishment.

(3) In case the PGW receives a downlink, DL, packet 505 towards a UErelated to the restarted SGW before the relevant PDN/MM contexts arere-established on a new SGW, step 302, the PGW selects step 304 a SGWand transmits step 308 a new GTP message 511 such as Paging request orreuse the existing message Downlink Data Notification message with newinformation elements according to an embodiment of the invention, namelythe IMSI and optional MME ID extensions, to the selected S-GW.

(4) The selected SGW transparently relays 513 the received pagingrequest message 511 to the MME indicated in the message 410 or all theMME/SGSN it is connected to 412.

(5) When the MME receives the paging request 513 for the UE related tothe restarted SGW, the MME shall trigger a paging request 517 usingS-TMSI or P-TMSI in the appropriate paging area.

(6) The UE performs the service request procedure 519 or send a LLCframe if the UE is camping in GERAN (GSM EDGE Radio Access Network).

(7) Steps 521 (Create session request (PGW ID, MME ID) from MME to SGW),523 (Modify bearer request MME ID) to PGW, 525 (Modify bearer response(PGW ID) to SGW) and 527 (Create session response (PGW ID)): The MMErelocates the UE to an available SGW and the MME indicates the currentlyused PGW to the selected SGW. The PGW will thus be able to forwarddownlink packets over the new user plane.

Populate MME/SGSN ID to PGW

A mentioned above, in some embodiments, the PGW needs to know the MME ID(IP address on control plane) for transmitting the Downlink DataNotification signal with the MME ID, in order for this signal to beforwarded to an identified MME (c.f. steps, 312, 313) for being used thecontrol plane signal 511, FIG. 5.

Hence, prior to the FIG. 5 signalling, the exemplary signallingembodiment shown in FIG. 6 may be completed.

In FIG. 6 an exemplary embodiment for establishing the relevant MMEidentification for the PGW and establishing the relevant PGWidentification for a new MME is shown.

More particularly, FIG. 6 shows a MME initiated updating of PGW duringAttach and Inter-MME TAU (Tracking Area Update) (option b), according tothe invention.

According to aspects of the invention, as shown in FIG. 6, the MME/SGSNID is one parameter to be included in the Paging Request from PGW, toallow the SGW to forward the paging request to the correct MME/SGSNwhere the UE is being served.

MME/SGSN may update the PGW with its network ID during Attach andInter-MME/SGSN mobility procedures. FIG. 6 is an example of suchupdating.

A new information element containing MME/SGSN ID may, according to theinvention, therefore be included in the Create Session Request 612/614during attach and RAU/TAU/handover with SGW relocation procedure and itmay also be included in Modify Bearer Request 624/626 during interMME/SGSN mobility procedure. For the inter MME/SGSN intra SGW mobilityprocedure, when there is no S5/S8 signalling available, to be able toupdate PGW MME/SGSN ID, one of options a), b) or c) above may be used.

Note that MME should also know the PGW ID in order to indicate to theSGW to select the currently used PGW during MT call recovery.

Among the advantages which may be accomplished according to embodimentsof the invention are: the duration of MT call service unavailability incase of a SGW restart is reduced; MT call successful rates in failurecases are increased; the robustness of the SAE/EPC system is improved.

To summarize, the following methods, entities and signals are providedaccording to embodiments of the invention:

A method for a packet gateway node, PGW (P-GW), being adapted forcommunicating with at least a serving gateway node, SGW (S-GW), the PGWbeing adapted for receiving and forwarding downlink data packets to auser entity, UE, the SGW moreover being adapted for communicating with amobility management entity, MME (MME/SGSN); comprising the steps of—when receiving a downlink user plane data packet 505 destined for theUE on a Packet Data Network, PDN, connection associated with a restartedSGW; —determining 302 if the PDN connection has not yet been relocatedto a new SGW and if so —selecting 304 at least one SGW, that is, therestarted SGW or another SGW; —transmitting 308 a control plane signal511 to the selected SGW, the control plane signal 511 identifying atleast the UE.

In further embodiments of the invention, the control plane signal is anindication of receiving downlink data for said UE. It may be a pagingrequest or a downlink data notification 511 or some other GTPv2 message.The control plane signal 511 may comprise an identity (IMSI) associatedwith the UE.

Moreover, the control plane signal 511 may comprise the identity of amobility management entity, MME (MME/SGSN), through which the PGWcommunicated with the UE before the SGW was restarted.

The PGW may moreover carry out the step of—receiving a create sessionrequest 614 or modify bearer request 626 with the identity of a mobilitymanagement entity, MME (MME/SGSN), updating the identity of a mobilitymanagement entity, MME (MME/SGSN) for subsequently using the identity ofa mobility management entity, MME (MME/SGSN) in the control plane signal511.

The steps of—selecting 304 at least one SGW, that is, the restarted SGWor another SGW, and—transmitting 308 a control plane signal 511 to theselected SGW, the control plane signal 511 identifying at least the UE,may be further being dependent on that—a bearer context, for which theuser plane data packet has been received, is preconfigured for allowingPGW initiated control plane signalling, based on operator policies, thatis, allowing—transmitting 308 the control plane signal 511 to theselected SGW, the control plane signal 511 identifying at least the UE.

As is understood from FIG. 5, before the step of —receiving a user planedata packet 505 destined for the UE on a PDN connection associated 300with a restarted SGW: —the UE is attaching 501 to the network comprisingthe PGW. As is also illustrated in FIG. 5 situation, the PGW keeps UEcontexts, that is, PDN Connection/Bearer contexts, relating to therestarted SGW, whereas the restarted SGW has lost its UE contexts.

If the downlink user plane data packet is not to be forwarded via arestarted SGW 301, —the PGW transmitting 306 the user plane data packetto the SGW.

Regarding the method for a serving gateway node, SGW: The SGW is beingadapted for communicating with at least a packet gateway node, PGW, theSGW and being adapted for receiving and forwarding downlink data packetsto a user entity, UE, the SGW communicating moreover communicating witha mobility management entity, MME. The method comprises the steps of —ifreceiving 406 a control plane signal 511 from the PGW identifying atleast the UE, —forwarding 410, 412 the control plane signal to aplurality of MME's the SGW is connected to or to a MME indicated in thecontrol plane signal 511.

This may be performed by the SGW carrying out the steps of —resolving408 whether an identity of a MME is provided, —if an identity of a MMEis provided, forwarding 410 the control plane signal 513 to theidentified MME, and —if not an identity of a MME is provided, forwarding412 the control plane signal 513 to a plurality of connected MME's.

The SGW when receiving 402 a user plane downlink data packet 105 to theUE—is transmitting 404 a control plane downlink data notification 108 tothe MME.

The control plane signal may be an indication of receiving downlink datafor said UE.

As mentioned in connection with the PGW the control plane signal may bea paging request or a downlink data notification 511 or another type ofGTPv2 signal.

The method for the SGW may moreover comprise the steps of—receiving andforwarding 414 a create session request 614 or modify bearer request 626with the identity of a mobility management entity, MME (MME/SGSN), tothe PGW.

Moreover, the control plane signal 511, 513 may be forwarded 513 by theSGW.

The PGW (P-GW) may be a Packet Data Network Gateway as is known in 3GPPstandards among others referred to in the background. The MME may be aMobility Management Entity/Serving gateway Support Node (MME/SGSN) andassociated identities are MME/SGSN identities.

There is also provided a method for a Mobility Management Entity, MME,wherein the MME is being adapted for inserting its MME identity (MME ID)in a Create Session Request signal 612 or in Modify Bearer RequestSignal 624.

Moreover, a signal is provided for a 3GPP a serving gateway node, S-GWor a PDN gateway node, P-GW, or a Mobility Management Entity, MME, theS-GW being adapted for communicating with at least a PDN gateway node,P-GW, and a user entity, UE, the signal being formatted as a CreateSession Request 612, 614 for use during attach and RAU/TAU/handover withSGW relocation procedure, or Modify Bearer Request 624, 626 during interMME/Serving Gateway Support Node mobility procedure, the signalcomprising an information element containing a Mobile Mobility EntityIdentity, MME ID/Serving Gateway Support Node identity, MME/SGSN ID.

There is also provided a Signal for a 3GPP a serving gateway node, S-GW,or a PDN gateway node, P-GW, or a Mobility Management Entity, MME, theP-GW and S-GW being adapted for communicating with one another, the S-GWbeing further adapted for communicating with a user entity, UE, via amobility management entity, MME, the signal being formatted as a GTPmessage 511, 513 such as Paging request or Downlink Data Notificationmessage with information elements corresponding to an InternationalMobile Subscriber Identity, IMSI, and/or a Mobile Mobility EntityIdentity, MME ID.

Furthermore there is provided according to embodiments of the invention:

A packet gateway node, PGW (P-GW), being adapted for communicating withat least a serving gateway node, SGW (S-GW), the PGW being adapted forreceiving and forwarding downlink data packets to a user entity, UE, theSGW moreover being adapted for communicating with a mobility managemententity, MME; the PGW being adapted for when receiving a downlink userplane data packet 505 destined for the UE on a Packet Data Network, PDN,connection associated with a restarted SGW; —determining 302 if the PDNconnection has not yet been relocated to a new SGW and if so —selecting304 at least one SGW, that is, the restarted SGW or another SGW;—transmitting 308 a control plane signal 511 to the selected SGW, thecontrol plane signal 511 identifying at least the UE.

PGW ma be adapted for—receiving a create session request 614 or modifybearer request 626 with the identity of a mobility management entity,MME (MME/SGSN), updating the identity of a mobility management entity,MME (MME/SGSN) for subsequently using the identity of a mobilitymanagement entity, MME (MME/SGSN) in the control plane signal 511.

For instance, the PGW is being a 3GPP Packet Data Network Gateway(P-GW).

A serving gateway node, SGW, is also provided, the SGW being adapted forcommunicating with at least a packet gateway node, PGW, the SGW andbeing adapted for receiving and forwarding downlink data packets to auser entity, UE, the SGW communicating moreover communicating with amobility management entity, MME; the SGW further being adapted for —ifreceiving 406 a control plane signal 511 from the PGW identifying atleast the UE,—forwarding 410, 412 the control plane signal to aplurality of MME's the SGW is connected to or to a MME indicated in thecontrol plane signal 511.

Serving gateway node, SGW, may also be adapted for—receiving andforwarding 414 a create session request 614 or modify bearer request 626with the identity of a mobility management entity, MME (MME/SGSN), tothe PGW.

As mentioned above the serving gateway node, SGW, may be a 3GPP ServingGateway (S-GW).

Finally, there is provided a Mobility Management Entity, MME, accordingto an embodiment of the invention, the MME being adapted for insertingits MME identity (MME ID) in a Create Session Request signal 612 or inModify Bearer Request Signal 624.

The Mobility Management Entity, MME, could be a 3GPP MME/S4-SGSN MME.

ABBREVIATIONS

eNB—E-UTRAN Node B

EPC—Evolved Packet Core

GTP—GPRS Tunnel Protocol

MM—Mobility Management

MME—Mobility Management Entity

MT—Mobile Terminating Call

PDN—Packet Data Network

P GW—PDN Gateway

SAE—System Architecture Evolution

S GW—Serving Gateway

TAI—Tracking Area Identity

TAU—Tracking Area Update

The invention claimed is:
 1. A method comprising: receiving at amobility management node (MMN) a first request transmitted by a userentity (UE); and after receiving the first request, the MMN transmitstowards a Packet Data Network (PDN) gateway node (PGW) a second requestcomprising information for enabling the PGW to recover a PDN connectionpreviously established for the UE, wherein the information for enablingthe PGW to recover the PDN connection comprises an MMN identifier foridentifying the MMN.
 2. The method of claim 1, wherein the first requestis one of an Attach Request and a Tracking Area Update (TAU) Request,the second request is one of a Create Session Request and a ModifyBearer Request.
 3. The method of claim 1, further comprising the MMNreceiving from a failed serving gateway (SGW) that has been restarted adownlink notification comprising a UE identifier for identifying a UE;in response to receiving the downlink notification comprising the UEidentifier, the MMN paging the UE; the MMN receiving a service requesttransmitted by the UE as a result of the MMN paging the UE; and inresponse to receiving the service request, the MMN generates a CreateSession Request comprising the MMN identifier for identifying the MMNand transmits the Create Session Request to the SGW.
 4. The method ofclaim 3, wherein the generated Create Session Request further comprisesa PGW identifier.
 5. A mobility management node (MMN), the MMNcomprising: a receiver; a transmitter; and a processing unit, comprisinga processor, coupled to the receiver and the transmitter, wherein theprocessing unit is configured such that, after the MMN receives a firstrequest transmitted by a user entity (UE), the processing unit causesthe MMN to transmit towards a Packet Data Network (PDN) gateway node(PGW) a second request comprising information for enabling the PGW torecover a PDN connection previously established for the UE, the firstrequest is one of an Attach Request and a Tracking Area Update Request,the second request is one of a first Create Session Request and a ModifyBearer Request, and the information for enabling the PGW to recover thePDN connection comprises an MMN identifier for identifying the MMN. 6.The MMN of claim 5, wherein the processing unit is further configuredsuch that: in response to the MMN receiving from a failed servinggateway (SGW) that has been restarted a paging request or downlink datanotification comprising a UE identifier for identifying the UE, theprocessing unit causes the MMN to page the UE, and in response to theMMN receiving from the UE a service request, the processing unitgenerates a second Create Session Request comprising the MMN identifierfor identifying the MMN and causes the MMN to transmit the second CreateSession Request.
 7. The MMN of claim 5, wherein the second CreateSession Request further comprises a PGW identifier.
 8. A methodcomprising: a mobility management node (MMN) receiving a first requestmessage transmitted by a user entity (UE), wherein the first requestmessage is one of an Attach Request and a Tracking Area Update (TAU)Request; and after receiving the first request message, the MMNtransmitting to a serving gateway (SGW) a second request messagecomprising information to be forwarded by the SGW to a Packet DataNetwork (PDN) gateway (PGW), the information to be forwarded by the SGWto the PGW comprising an MMN identifier identifying the MMN, wherein thesecond request message is one of a first Create Session Request and aModify Bearer Request, and the second request message comprises aplurality of Information Elements (IEs) including an MMN identifier IEcontaining the MMN identifier identifying the MMN.
 9. The method ofclaim 8, further comprising: receiving a downlink notification messagecomprising a UE identifier for identifying a UE, wherein the downlinknotification message was forwarded by an SGW to the MMN as a result ofthe SGW receiving a downlink notification message transmitted by a PGWin response to the PGW receiving downlink data for the identified UE.10. The method of claim 9, further comprising: in response receiving thedownlink notification message, the MMN paging the identified UE; and inresponse to the MMN receiving from the UE a service request, the MMNgenerating a second Create Session Request comprising the MMN identifierand transmitting the second Create Session Request.
 11. The method ofclaim 9, wherein the UE identifier is an International Mobile SubscriberIdentity (IMSI).
 12. The method of claim 9, wherein the second requestmessage further comprises a PGW identifier.
 13. The method of claim 8,wherein the MMN comprises a 3GPP Mobility Management Entity (MME). 14.The method of claim 8, wherein the first request message is the AttachRequest, and the second request message is the first Create SessionRequest.
 15. The method of claim 8, wherein the first request message isthe TAU Request, and the second request message is the Modify BearerRequest.
 16. A mobility management node (MMN), the MMN comprising: areceiver for receiving a first request message transmitted by a userentity (UE), wherein the first request message is one of an AttachRequest and a Tracking Area Update (TAU) Request; a transmitter; and aprocessing unit, comprising a processor, coupled to the receiver and thetransmitter, wherein the MMN is configured to: after receiving the firstrequest message, employ the transmitter to transmit to a serving gateway(SGW) a second request message comprising information to be forwarded bythe SGW to a Packet Data Network (PDN) gateway (PGW), the information tobe forwarded by the SGW to the PGW comprising an MMN identifieridentifying the MMN, wherein the second request message is one of afirst Create Session Request and a Modify Bearer Request, and the secondrequest message comprises a plurality of Information Elements (IEs)including an MMN identifier IE containing the MMN identifier identifyingthe MMN.
 17. The MMN of claim 16, wherein the MMN is operable to receivea downlink notification message comprising a UE identifier foridentifying a UE, wherein the downlink notification message wasforwarded by an SGW to the MMN as a result of the SGW receiving adownlink notification message transmitted by a PGW in response to thePGW receiving downlink data for the identified UE.
 18. The MMN of claim17, wherein the MMN is further configured such that, in responsereceiving the downlink notification message, the MMN pages theidentified UE; and the MMN is further configured such that, in responseto the MMN receiving from the UE a service request, the MMN generates asecond Create Session Request comprising the MMN identifier andtransmits the second Create Session Request.
 19. The MMN of claim 17,wherein the UE identifier is an International Mobile Subscriber Identity(IMSI).